MEXICO CITY – The mystery surrounding the murder of the brother of a former president, Carlos Salinas de Gortari, is becoming a national obsession, with the twin revelations that the victim wrote a despondent note shortly before his death and that he was under investigation in France for allegedly laundering money.

Carlos Salinas' youngest brother, Enrique, had stayed largely out of the limelight for years until his body was discovered in a family car parked on a residential suburban street. His head had been shoved in a yellow plastic bag and he had been strangled.

There were bruises on Salinas' face, suggesting that his killers had blindfolded and punched him before he died. He was 52, a multimillionaire engineer with cash-flow problems, a divorced wife and three grown children, investigators said.

The murder comes four years after the ex-president's elder brother, Raúl, a colorful businessman who grew rich during Carlos Salinas' administration, was convicted of ordering the murder of his former brother-in-law and sent to prison, shattering the impunity that the rich and powerful once enjoyed in Mexico.

Raúl Salinas' business dealings have long been a subject of investigation here and in Europe because of allegations that government funds and ill-gotten drug profits ended up in his bank.

Enrique Salinas and his former wife lived in Paris during the 1990s. Since 1996, French authorities have been investigating what role, if any, they played in helping Raul Salinas move large amounts of money between banks, according to a French judicial official.

French police recently visited the Salinases' apartment in Paris to try to inform Enrique Salinas that he was going to be charged with laundering money by buying property in France with funds from embezzlement schemes and drug dealing, Notimex, the official news agency of the Mexican government, reported Thursday. Not finding him, French authorities put an alert out through Interpol on Nov. 22, asking Mexican police to locate him, prosecutors here said.

What all this has to do with Salinas' death early Monday is unclear, but speculation has dominated the capital's rumor mill and talk radio. Mexican authorities are still treating the death as a failed attempt to extort information or money from Salinas, discounting any link to Raúl Salinas or money transfers.

On Thursday, the Mexico state prosecutor in charge of the investigation, Alfonso Navarrete Prida, released an unsigned note, apparently in Salinas' handwriting, that he said was found on the body. The note said Salinas, his family and his children had been threatened by unnamed people.

The note said that since 1995, someone had been harassing Salinas, making it impossible for him to continue doing business. It goes on to say the harassment had affected his business partners and his children, "who have had to confront a great risk to their security, both physical and emotional."

Though the note sounds suicidal, prosecutors are sure Salinas was murdered. For starters, forensic evidence shows he was suffocated somewhere outside his car, then put in the car and driven to the suburb. Security cameras caught images of his killers, a group the police say may number as many as six, leaving the scene in a black sport utility vehicle. Hair found in the victim's hands and the bruises suggest that he had struggled with his attackers.

The death is the latest chapter in the saga of a once all-powerful family in the former ruling party whose story has become a slow-motion train wreck since President Salinas left office in December 1994.

Weeks after he left office, the economy collapsed, poisoning Carlos Salinas' legacy as a visionary modernizer.

In 1999, Raúl Salinas was convicted of orchestrating the 1994 murder of a prominent politician who was also his brother-in-law.

Now, Enrique Salinas has died just before he was to face charges of money-laundering.

"Misterio," screamed the headline of El Gráfico Thursday, while talk-radio hosts bantered about possible motives. Most went along with the theory of extortion that Navarrete first proposed. Others raised the possibility of a political murder, even a crime of passion.

On Friday, Navarrete said the investigation was was focusing on a close circle of friends and associates, as well as the victim's financial troubles.

The killing occurred about a week after the news magazine Proceso published an article describing the "hidden wealth" of the Salinas family. The article focused on descriptions of European bank accounts with millions of dollars that were mentioned in a divorce agreement promising Salinas' ex-wife large sums of money and on several properties listed in his name in posh neighborhoods of Mexico City.

Some of those European accounts had been frozen by French and Swiss authorities due to investigations into possible money laundering.

Raúl Trejo Delarbre, a professor who analyzes Mexican news, said the public fascination with the story was natural because it involved the Salinas de Gortari family. "It's a surname associated with an important chapter of Mexico's history, " he said, "but overall, as everyone knows, with strong accusations that have never been cleared up, and for this reason, with a family persecuted by bad luck."